/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with this
 * work for additional information regarding copyright ownership. The ASF
 * licenses this file to You under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package org.apache.commons.exec;

import org.apache.commons.exec.util.DebugUtils;

/**
 * Destroys a process running for too long. For example:
 * 
 * <pre>
 * ExecuteWatchdog watchdog = new ExecuteWatchdog(30000);
 * Executer exec = new Executer(myloghandler, watchdog);
 * exec.setCommandLine(mycmdline);
 * int exitvalue = exec.execute();
 * if (Execute.isFailure(exitvalue) &amp;&amp; watchdog.killedProcess()) {
 * 	// it was killed on purpose by the watchdog
 * }
 * </pre>
 * 
 * When starting an asynchronous process than 'ExecuteWatchdog' is the keeper of
 * the process handle. In some cases it is useful not to define a timeout (and
 * pass 'INFINITE_TIMEOUT') and to kill the process explicitly using
 * 'destroyProcess()'.
 * <p>
 * Please note that ExecuteWatchdog is processed asynchronously, e.g. it might
 * be still attached to a process even after the DefaultExecutor.execute has
 * returned.
 * 
 * @see org.apache.commons.exec.Executor
 * @see org.apache.commons.exec.Watchdog
 */
public class ExecuteWatchdog implements TimeoutObserver {

	/** The marker for an infinite timeout */
	public static final long INFINITE_TIMEOUT = -1;

	/** The process to execute and watch for duration. */
	private Process process;

	/** Is a user-supplied timeout in use */
	private final boolean hasWatchdog;

	/** Say whether or not the watchdog is currently monitoring a process. */
	private boolean watch;

	/** Exception that might be thrown during the process execution. */
	private Exception caught;

	/** Say whether or not the process was killed due to running overtime. */
	private boolean killedProcess;

	/** Will tell us whether timeout has occurred. */
	private final Watchdog watchdog;

	/**
	 * Creates a new watchdog with a given timeout.
	 * 
	 * @param timeout
	 *            the timeout for the process in milliseconds. It must be
	 *            greater than 0 or 'INFINITE_TIMEOUT'
	 */
	public ExecuteWatchdog(final long timeout) {
		this.killedProcess = false;
		this.watch = false;
		this.hasWatchdog = (timeout != INFINITE_TIMEOUT);
		if (this.hasWatchdog) {
			this.watchdog = new Watchdog(timeout);
			this.watchdog.addTimeoutObserver(this);
		} else {
			this.watchdog = null;
		}
	}

	/**
	 * Watches the given process and terminates it, if it runs for too long. All
	 * information from the previous run are reset.
	 * 
	 * @param process
	 *            the process to monitor. It cannot be <tt>null</tt>
	 * @throws IllegalStateException
	 *             if a process is still being monitored.
	 */
	public synchronized void start(final Process process) {
		if (process == null) {
			throw new NullPointerException("process is null.");
		}
		if (this.process != null) {
			throw new IllegalStateException("Already running.");
		}
		this.caught = null;
		this.killedProcess = false;
		this.watch = true;
		this.process = process;
		if (this.hasWatchdog) {
			watchdog.start();
		}
	}

	/**
	 * Stops the watcher. It will notify all threads possibly waiting on this
	 * object.
	 */
	public synchronized void stop() {
		if (hasWatchdog) {
			watchdog.stop();
		}
		watch = false;
		process = null;
	}

	/**
	 * Destroys the running process manually.
	 */
	public synchronized void destroyProcess() {
		this.timeoutOccured(null);
		this.stop();
	}

	/**
	 * Called after watchdog has finished.
	 */
	public synchronized void timeoutOccured(final Watchdog w) {
		try {
			try {
				// We must check if the process was not stopped
				// before being here
				if (process != null) {
					process.exitValue();
				}
			} catch (IllegalThreadStateException itse) {
				// the process is not terminated, if this is really
				// a timeout and not a manual stop then destroy it.
				if (watch) {
					killedProcess = true;
					process.destroy();
				}
			}
		} catch (Exception e) {
			caught = e;
			DebugUtils.handleException(
					"Getting the exit value of the process failed", e);
		} finally {
			cleanUp();
		}
	}

	/**
	 * This method will rethrow the exception that was possibly caught during
	 * the run of the process. It will only remains valid once the process has
	 * been terminated either by 'error', timeout or manual intervention.
	 * Information will be discarded once a new process is ran.
	 * 
	 * @throws Exception
	 *             a wrapped exception over the one that was silently swallowed
	 *             and stored during the process run.
	 */
	public synchronized void checkException() throws Exception {
		if (caught != null) {
			throw caught;
		}
	}

	/**
	 * Indicates whether or not the watchdog is still monitoring the process.
	 * 
	 * @return <tt>true</tt> if the process is still running, otherwise
	 *         <tt>false</tt>.
	 */
	public synchronized boolean isWatching() {
		return watch;
	}

	/**
	 * Indicates whether the last process run was killed.
	 * 
	 * @return <tt>true</tt> if the process was killed <tt>false</tt>.
	 */
	public synchronized boolean killedProcess() {
		return killedProcess;
	}

	/**
	 * reset the monitor flag and the process.
	 */
	protected synchronized void cleanUp() {
		watch = false;
		process = null;
	}
}
